1. Field of the Invention
The present invention relates to a battery remaining capacity detection method and a power supply apparatus, and more particularly to a remaining capacity detection method and a power supply apparatus that detect a remaining capacity of a battery contained in a power supply apparatus for driving a motor for running vehicles, for example.
2. Description of the Related Art
A battery remaining capacity (state-of-charge (SOC) is typically detected by subtracting a discharge amount from a full-charged state. The discharge amount is calculated by integrating a discharge current. The battery remaining capacity is displayed as the product of current and time, i.e., Ah, or as the rate (%) relative to the full-charged capacity defined as 100% that is an amount (Ah) when a battery is fully charged. In either display state of remaining capacity, it is detected by subtracting a discharged amount from the full-charged state. However, the remaining capacity that is detected based on the integrated value of discharged current does not always agree with a correct remaining capacity of battery. The reason is that the amount of current or temperature causes an error of remaining capacity detection.
A method disclosed in Japanese Laid-Open Patent Publication TOKUKAI No. SHO 56-126776 has been developed to provide an amount detection method that precisely detects the amount of battery for vehicles even in the operation of vehicles. In this method, battery discharge current values at a plurality of different times when different values are obtained in the discharging with a large amount of current, and battery voltage terminal values when the respective currents are discharged are detected. The internal resistance and the voltage of the battery are calculated based on the detected current and voltage value. The battery capacity is calculated based on the calculated internal resistance and voltage by using a function that represents correlation among a previously and experimentally obtained battery capacity and an internal resistance and an voltage.
However, in some batteries used for power supply, a memory effect occurs, and thus may cause difficulty of remaining capacity detection. The memory effect is a phenomenon where, in the case where a nickel-cadmium battery, nickel-hydrogen battery or the like is cyclically charge/discharged from/to a shallow depth of discharge, its discharge voltage temporarily decreases when discharged to a deep depth of discharge. Since the remaining capacity of battery varies due to a memory effect, the remaining capacity of battery cannot be precisely estimated. If the remaining capacity is improperly detected, the battery may have an overload in charging/discharging operation. This may cause remarkable deterioration of battery life.
On the other hand, the remaining capacity varies due to battery self discharging. These factors cause difficulty of estimation of battery remaining capacity. For this reason, it is very difficult to precisely ascertain the remaining capacity.
The present invention is aimed at solving the problems. It is a main object of the present invention is to provide a battery remaining capacity detection method and a power supply apparatus capable of more precisely detecting a battery remaining capacity.